1. Field of the Invention
The present invention relates to a droplet discharging method and apparatus, and more particularly, to a droplet discharging method and apparatus whereby a liquid, such as ink with high viscosity, or the like, can be discharged at a sufficient speed in the form of a minute droplet, by means of an inkjet method.
2. Description of the Related Art
A droplet discharging apparatus according to an inkjet method records images, or the like, by discharging a liquid, such as ink, or the like, towards a recording medium, as droplets, from nozzles formed on the recording head. There are various ink discharging methods for an ink droplet discharging apparatus based on an inkjet method, and a method is known, for example, whereby the volume of a pressure chamber is caused to change by means of deformation of a piezoelectric ceramic, ink is provided into the pressure chamber from an ink supply passage when the volume is increased, and the ink inside the pressure chamber is discharged from the nozzle as a droplet when the volume of the pressure chamber is reduced.
In an ink droplet discharging apparatus of this kind, in order to increase the resolution of the recording, it is necessary to discharge ink droplets of small volume, and hence various means for achieving this have been implemented. For example, a method is known wherein an ink droplet is torn off, thereby miniaturizing the size of the propelled ink droplet, by pulling back a portion of an ink droplet that is about to be propelled from a nozzle, by applying a subsequent additional drive waveform to an actuator for changing the volume of the pressure chamber, after a drive waveform for discharging ink has been applied (for example, see Japanese Patent Application Publication No. 11-170515).
Moreover, as described above, the drive waveform for discharging ink is applied to the actuator which changes the volume of the pressure chamber, and subsequently, an additional drive waveform for miniaturizing the ink droplet is applied, whereupon a drive waveform for stabilizing the vibrating state of the meniscus face of the ink is further applied, and in such a manner that the speed of the droplet of ink discharged subsequently is prevented from declining (for example, see Japanese Patent Application Publication No. 11-227203).
However, both of the cases disclosed in the reference patents described above are premised on the fact that the ink inside the pressure chamber performs vibration (intrinsic vibration) according to a natural period, ink droplets being miniaturized before discharging by utilizing this intrinsic vibration in the case of the method according to Japanese Patent Application Publication No. 11-170515, and the meniscus face of the ink being stabilized by means of a subsequently applied stabilizing waveform (pulse), as described above, if the viscosity is low due to high temperature, by utilizing this intrinsic vibration, in the case of the method according to Japanese Patent Application Publication No. 11-227203, so that both cases are premised on the intrinsic vibration of the meniscus face, and the discharge timing is controlled by a drive waveform which utilizes this intrinsic vibration, then the design of the drive waveform is subject to temporal restrictions and cycle-related restrictions, and hence improvements are desired.
In general, as the viscosity of a liquid increases, the resisting force directly proportional to the flow rate of the liquid also increases. Consequently, in the case of high viscosity in a conventional ink droplet discharging apparatus as described above, then if a droplet is discharged by driving the actuator under the same drive conditions as a low-viscosity liquid, the speed of the propelled droplet declined in accordance with the aforementioned resisting force. Moreover, if the viscosity of the ink is high, then the refilling of the ink after discharge of the ink droplet will be slow, and consequently, it will take a long time to return to the initial state after discharging of the ink, and hence the recording (printing) speed will decline.